Methods of rolling molybdenum and molybdenum alloys



United States Patent METHODS OF ROLLING MOLYBDENUM AND MOLYBDENUM ALLOYS Edgar S. Byron, Bloomfield, and Robert F. Baker, Butler, N. J., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy No Drawing. Application June 24, 1953, Serial No. 363,918

4 Claims. (Cl. 148-115) This invention relates to a new method for rolling molybdenum and molybdenum alloys.

The successful rolling of molybdenum and its alloys is dependent upon a number of controlling factors attendant to the process. Such factors as rolling at maximum plasticity, the rolling-annealing schedule, temperatures, times, etc., are controlling for the production of a product of satisfactory hardness, strength and bending yield. For example, it has been found that if molybdenum and its alloy containing 0.10% cobalt are rolled above the maximum plasticity temperature range (about 1300-1500 C.) they tend to become hot short. As another example, the anneal time in the rolling schedule is highly controlling as is evident from the fact that if the metal is overheated or underheated in the process the ingot will break during rolling, so that the problem becomes one of heating sufficiently to relieve the stresses so that overstressing the material in the succeeding passes is avoided and yet not heating to such an extent that the yield strength and tensile strength developed in the preceding passes is undesirably lowered. Other factors are equally important.

In addition to the production of a product having maximum hardness, strength and bending yield, the process should give consistent and reproducible results and yield products having uniform properties so that the process will be adaptable for large scale production.

It is therefore an object of the present invention to provide a process for rolling molybdenum and its alloys which gives maximum reduction in cross-sectional area with the production of a product having acceptable hardness, strength and bending yield.

It is another object of the invention to provide a process as stated above which gives consistent and reproducible results and provides finished products having uniform properties.

The following examples are illustrative of the invention but are not limiting. The anneal times in all schedules appear to be critical. The elapsed time between successive passes taken without reheating should be held to a minimum. Ingots are rotated 90 between successive passes.

Example I In the following example a 21 inch diameter mill and a rolling speed of 52 R. P. M. was used to reduce the cross-sectional area of the ingot approximately 56%. A 1 x 1 ingot of molybdenum containing 0.10% cobalt was heated to between 1420 and 1480 C. and rolled to reduce the cross-sectional area to 2.40 square inches in the first pass (approximately 88% of the original cross-sectional area). Without reheating the ingot was rerolled to a cross-sectional area of 2.16 square inches in the second pass (approximately 79% of the original cross-sectional area). Annealing was accomplished by heating for 5 minutes above 1350 C., preferably between 1350 and 1400 C. In the third pass the ingot was rolled to an area of 1.89 square inches at 13701420 C. (approximately 69% of the original cross-sectional area). In the fourth pass it was rerolled without reheating to an area of 1.62 square inches (approximately 59% of the original cross-sectional area). The ingot was then annealed by heating for 2 minutes above 1300 C., preferably between 1300l350 C. In the fifth pass the ingot was rolled to an area of 1.39 square inches at 1340-1370" C. (approximately 51% of the original crosssectional area) and in the sixth and final pass it was rolled without reheating to an area of- 1.25 square inches (approximately 44% of the original cross-sectional area).

Rods of molybdenum containing 0.10% cobalt, 1% inch square by 30-35 inches long were produced using the above schedule. They had the following properties: Hardness230250 V. P. N. (Vickers pyramid number); strength120l48% of an arbitrary standard; yield in bending-2248 mils. By way of comparison it is noted that heat-treated or sintered material has a strength value of approximately of an arbitrary standard.

Example II Ingots of pure molybdenum of an area of 1 x 1 were reduced approximately 56% in area by using the following schedule. On the first pass, taken at 1420-1480 C. the cross-sectional area was reduced to 2.40 square inches (2. reduction to approximately 88% of the original cross-sectional area). Without reheating the ingot was given four more passes reducing the area to 2.02, 1.72, 1.49 and 1.23 square inches, respectively (a reduction to approximately 74%, 63%, 54% and 44%, respectively, of the original cross-sectional area). Pure molybdenum ingots were rolled in this manner to finish bars 1 /8" square by 3035 inches in length with the following properties: hardness215230 V. P. N.; strength 170-200% of an arbitrary standard, and yield in bending4660 mils.

Example 111 In working larger bars of pure molybdenum a slight modification of the above schedule was used. An overall reduction of approximately 73% was obtained in a 21 inch diameter mill. An ingot, 2%" x 2% in crosssection was rolled as follows: On the first pass at 1470-1520" C. the area was reduced to 3.95 square inches (a reduction to approximately 92% of the original crosssectional area). Without reheating the ingot was rerolled on the second pass to an area of 3.24 square inches (a reduction to approximately 72% of the original cross sectional area). Both of the above passes were made at a roll speed of 40 R. P. M. After the second pass the ingot was annealed by heating for 5 minutes above 1350 C., preferably between 1350 and 1400 C. With the roll speed increased to 52 R. P. M. the ingot was reduced in the third pass to an area of 2.60 square inches at a temperature of 1420-1480" C. (a reduction to approximately 58% of the original cross-sectional area). At the same roll speed and without reheating, the ingot was given five more passes reducing the area to 2.22, 1.89, 1.62, 1.39 and 1.25 square inches, respectively (a reduction in cross-sectional area to approximately 49%, 42%, 36%, 31% and 27%, respectively, of the original cross-sectional area).

Using the above schedule, rods of pure molybdenum 1%" square by 66-72 inches in length were produced having the following properties: hardness200-220 V. P. N., strength--l45% of an arbitrary standard, and yield in bending-2030 mils.

It is thus seen that the invention provides a process for rolling molybdenum and its alloys by which a maximum of reduction in cross-sectional area is obtained and which gives a product meeting acceptable standards of hardness, strength and yield in bending. It is an advanrolling without reheating to reduce the cross-sectional area to approximately 79% of the original cross-sectional area, (3) annealing by heating for five minutes at a temperature between about13'50 C. and 1400 C., (4) rolling between 1370-1420 C.:to reduce the cross-sectional area to approximately 69% of the original cross-sectional area, (5) rerollingwithout reheating to reduce the crosssectional area to approximately 59% of the original crosssectional area, (6) annealing by heating for 2 /2 minutes at a temperature of between about 71300 C. and 1350 C., (7) rolling between 13401370 C. to reduce the cross-sectional area to'approximately 51% of the original cross-sectional area and (8) rerolling without reheating to reduce the cross-sectional area to approximately 44% of the original cross-sectional area.

2. The process of claim 1 in which'the ingot is turned 90 between successive passes.

3. The process of working ingots of molybdenum which comprises reducing the crosseeetional area of the bar approximately 73% according to the following schedule: (1) rolling at 14701520 C. to reduce the cross-sectional area to approximately 92% of the original cross-sectional area, (2) rerolling without reheating to reduce the crosssectional area to approximately 72% of the original crosssectional area, ('3 annealing by heating for five minutes at a temperature between about 1350" and 1400 C., (4) rolling at 142()l480 C. to reduce the cross-sectional area to approximately 58% of the original cross-sectional area, (5') and rerol-ling without reheating in five successive passes to reduce the cross-sectional area to approximately 42%., 36% and 27% respectively, of the' original cross-sectionalarea. y

4. The process of claim 3-in which the ingot is turned between successive passes; 4

References Citedin the fileof this patent UNITED STATES PATENTS 2,666,721 Bechtold et a1 Ian. 19, 1954 FOREIGN PATENTS 114,282 Great Britain Mar. 28,1918 

1. THE PROCESS OF WORKING INGOTS OF MOLYBDENUM AND MOLYBDENUM-COBALT ALLOYS CONTAINING A MAJOR PROPORTION OF MOLYBDENUM WHICH COMPRISES REDUCING THE CROSS-SECTIONAL AREA OF THE INGOT BY APPROXIMATELY 56% ACCORDING TO THE FOLLOWING SCHEDULE: (1) ROLLING BETWEEN 14201480* C. TO REDUCE THE CROSS-SECTIONAL AREA TO APPROXIMATELY 88% OF THE ORIGINAL CROSS-SECTIONAL AREA, (2) REROLLING WITHOUT REHEATING TO REDUCE THE CROSS-SECTIONAL AREA TO APPROXIMATELY 79% OF THE ORIGINAL CROSS-SECTIONAL AREA, (3) ANNEALING BY HEATING FOR FIVE MINUTES AT A TEMPERATURE BETWEEN ABOUT 1350* C. AND 1400* C., (4) ROLLING BETWEEN 1370-1420* C. TO REDUCE THE CROSS-SECTIONAL AREA TO APPROXIMATELY 69% OF THE ORIGINAL CROSS-SECTIONAL AREA, (5) REROLLING WITHOUT REHEATING TO REDUCE THE CROSSSECTIONAL AREA TO APPROXIMATELY 59% OF THE ORIGINAL CROSSSECTIONAL AREA, (6) ANNEALING BY HEATING FOR 21/2 MINUTES AT A TEMPERATURE OF BETWEEN ABOUT 1300* C. AND 1350* C., (7) ROLLING BETWEEN 1340-1370* C. TO REDUCE THE CROSS-SECTIONAL AREA TO APPROXIMATELY 51% OF THE ORIGINAL CROSS-SECTIONAL AREA AND (8) REROLLING WITHOUT REHEATING TO REDUCE THE CROSS-SECTIONAL AREA TO APPROXIMATELY 44% OF THE ORIGINAL CROSS-SECTIONAL AREA. 